Method for producing bubble domains in magnetic film-substrate structures

ABSTRACT

A METHOD FOR PRODUCING A BUBBLE DOMAIN IN A MAGNETIC SINGLE CRYSTAL GARNET FILM-SUBSTRATE IS DISCLOSED. THE METHOD INVOLVES THE EPITAXIAL DEPOSITION OF AN IRON GARNET FILM OF THE PROPER CRYSTALLOGRAPHIC ORIENTATION AND HAVING A POSITIVE MAGNETOSTRICTION CONSTANT ON A GARNET SUBSTRATE IN WHICH THE ROOM TEMPERATURE LATTICE CONSTANT OF THE FILM IS LARGER THAN THE ROOM TEMPERATURE LATTICE CONSTANT OF THE SUBSTRATE, PREFERABLY BY AN AMOUNT LESS THAN 0.035 ANGSTROM.

July 10, 1973 J. E. MEE ETAL 3,745,045

. METHOD FOR PRODUCING BUBBLE DOMAINS IN MAGNETIC FILM-SUBSTRATE STRUCTURES Filed Dec. 28, 1970 INVENTORS MEE United States Patent Calif.

Filed Dec. 28, 1970, Ser. No. 101,785 Int. Cl. H01f /06 US. Cl. 117-235 7 Claims ABSTRACT OF THE DISCLOSURE A method for producing a bubble domain in a magnetic single crystal garnet film-substrate structure is disclosed. The method involves the epitaxial deposition of an iron garnet film of the proper crystallographic orientation and having a positive magnetostriction constant on a garnet substrate in which the room temperature lattice constant of the film is larger than the room temperature lattice constant of the substrate, preferably by an amount less than 0.035 angstrom.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to bubble domains and more particularly to a method of forming a craze-free film having bubble domains therein.

(2) Description of prior art Magnetic bubble domains in a sheet of magnetic medium, such as yttrium orthofern'te, are Well known in the art and are described in US. Pat. No. 3,460,116 and others. Magnetic bubble domains in composite structures having a thin film of a single crystal iron garnet on an oxide substrate are disclosed in the co-pending patent applications to Mee et al., US. Ser. Nos. 16,446, filed Mar. 4, 1970 and now US. Pat. No. 3,645,788 and 16,447 filed Mar. 4, 1970. These co-pending patent applications are incorporated herewith.

Some of the bubble domain composite single crystal film-substrate structures reported in the prior art have had crazing, that is cracking, of the film, making them unsuitable for certain types of bubble domain device applications. Other iron garnet film-substrate structures were observed to have domains whose magnetization directions are in the plane of the film in contrast to the desired bubble domains whose magnetization directions are perpendicular to the plane of the film.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide an improved method of forming a single crystal iron garnet film-substrate structure having bubble domains therein.

It is another object of this invention to provide a meth- 0d of forming a bubble domain film-substrate structure having a craze-free film surface.

These and other objects of this invention are accomplished by a method in which the uniaxial anisotropy necessary for bubble domain formation in a craze-free film-substrate structure is afiected by proper control of the mechanical stress present in the film at room temperature. A specific step in the method involves depositing a single crystal iron garnet film of the proper crystallo graphic orientation and having a positive magnetostriction constant on a substrate in which the room temperature lattice constant of the film is larger than the room temperature lattice constant of the substrate preferably by an amount less than 0.035 angstrom.

3,?45046 Patented July I0, 1973 'ice BRIEF DESCRIPTION OF THE DRAWING The drawing shows a magnetic bubble domain film-sub strate structure made in accordance with the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION This invention involves a process in which a single crystal iron garnet material is chemically vapor deposited to form a film on a substrate. It is necessary that the single crystal material have the proper crystallographic orientation to take advantage of the positive magnetostriction. In addition the room lattice constant of the deposited film is larger than the room lattice constant of the substrate by an amount less than 0.035 angstrom. The resultant film-substrate structure has a craze-free film with bubble domains therein.

In general, the normal source of uniaxial anisotropy observed in magnetic materials is the crystal structure of the material When single crystal platelets with positive magnetostriction constants (A A 0), are under stress, the magnetostriction contribution tends to make the normal to the plane of the platelet an easy axis of magnetization if the platelet is in compression (6 O), and a hard axis if the platelet is intension (6 0) where A and A are the saturation values of the linear magnetostriction constants along the 100 and ll1 directions, respectively, and 0' is the stress in the plane of the material.

The room temperature magnetostriction constants of selected iron garnets are listed in the following table.

Magnetostriet-ion constant Iron garnet Amoun M1100 S1113F05012 +21 8 5 EmFeSOm +21 +1. 8 GdaFeson. O 3. 1 Tb3Fe50r2 -3. 3 +12 Dy3Fe O z -12. 5 -5. 9 HOJF85012. -3. 4 -4. U El3Fe50lZ- +2. 0 4. 9 TrnaFesoiz +1. 4 5. 2 Yb3F650i2- +1. 4 4 5 YaFesOm -1. 4 -2 4 Y3Gao.a4Fei.3uO z- 1. 4 -1 7 LugFesom 1. 4 -2 4 Some of these iron garnet materials, for example,

Tb F65O12 and Yb Fe O have both a negative and a positive magnetostriction constant. In the practice of this invention the crystallographic orientation of the garnet film must be chosen to take advantage of the positive magnetostriction constant. In the case with Tb -R 0 material, the orientation would be {111}. With the Yb Fe O material, the orientation would be {100}.

The values of the magnetostriction constants of the iron garnet material, as well as its magnetization, can be varied by depositing a film containing a mixture of two or more pure iron garnets and/or by substituting other cations for iron ions.

It is understood that whether there is mixing and/or substitution or not, the condition for bubble domain formation in the iron garnet material, H /41rM 1, has to be satisfied, where H is the uniaxial anisotropy field and 41rM is the magnetization.

In magnetic oxide film-substrate structures formed by chemical vapor deposition, the dominant source of uniaxial anisotropy is the magnetostrictive effect resulting from the stress existing in the film. This stress is due to the difference between the lattice constants and the thermal expansion coefficients of the film and substrate and may be in the form of tension or compression.

This invention specifically covers a method of forming a bubble domain structure by depositing a magnetic single crystal garnet film of the proper orientation and having a positive magnetostriction constant on a substrate in which the film is in compression.

A co-pending application to Mee et al., Ser. No. 101,- 786, filed Dec. 28, 1970 covers a method of forming a bubble domain structure by depositing a magnetic single crystal garnet film of the proper orientation and having a negative magnetostriction constant on a substrate in which the film is in tension.

A co-pending application to Mee et al., Ser. No. 101,- 787, filing date Dec. 28, 1970 covers a second method of forming a bubble domain structure "by depositing a magnetic single crystal garnet film of the proper orientation and having a negative magnetostriction constant on a substrate in which the film is in tension.

As shown in the drawing, an oxide substrate' 10 is preferably subjected to a chemical vapor deposition step to provide a thin film of magnetic bubble domain material, film 12. The deposition step is carried out in accordance with the co-pending application, Ser. No. 833,- 268 filed June 16, 1969 and now abandoned, and assigned to the assignee of the present invention. This pending patent application is incorporated herewith by reference hereto. The film 12 may be deposited by sputtering techniques or by a liquid phase epitaxial process.

The substrate 10 is monocrystalline garnet having a J Q O formulation wherein the J constituent of the wafer formulation is at least one element selected from the group consisting of cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, lanthanum, yttrium, calcium, and bismuth; and the Q constituent of the wafer formulation is at least one element selected from the group consisting of indium, gallium, scandium, titanium, vanadium, chromium, manganese, rhodium, zirconium, hafnium, niobium, tantalum, aluminum, phosphorus, arsenic and antimony.

Examples of substrate materials are mixed yttrium gadolinium gallium garnet, gadolinium gallium garnet, aluminum substituted gadolinium gallium garnet, terbium gallium garnet, samarium gallium garnet, and dysprosium gallium garnet.

The film of the bubble domain material is a single crystal garnet film having a J Q O formulation wherein the I constituent of the film formulation has at least one element selected from the group of cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, erbium, thulium, ytterbium, and lanthanum; the Q constituent of the film formulation is taken iron and gallium, iron and indium, iron and scandium, iron and titanium, iron and vanadium, iron and chromium, and iron and manganese.

A preferred substrate material is samarium gallium garnet when the film material is terbium iron garnet.

In accordance with this invention, an iron garnet film of the proper orientation and having a positive magnetostriction constant is deposited on a garnet substrate in which the room temperature lattice constant of the film is larger than the room temperature lattice constant of the substrate, preferably by an amount less than 0.035 angstrom. The preferred difference between the lattice constants is of the order of 0.010 to 0.025 angstrom. When the lattice constant difference is about 0.035 angstrom or more, the compressive stress is so great that the compression relieves itself and the film is in tension due to the thermal expansion mismatch. When the film lattice constant is smaller than the substrate lattice constant, the film is in tension and there are no bubble domains since the normal to plane of the film is the hard magnetization axis and the domain magnetizations lie in the plane.

As previously discussed, the difference in the coefiicients of thermal expansion between the film and the substrate contributes to the total stress present in the film. The thermal expansion stress contribution is within acceptable limits as long as the coeflicient of thermal expansion of the substrate does not differ from that of the film by more than 1X10 C. between 25 C. and 1200 C. A certain amount of mismatch between film-substrate room temperature lattice constants and/or thermal ex pansion characteristics is required in order to provide the stress which produces the uniaxial anisotropy necessary for bubble domain formation. If film and substrate are too closely matched in both lattice constant and thermal expansion, the proper stress necessary for bubble domain formation will not be achieved.

Example I A [111] film of terbium iron garnet, T-b Fe O having a lattice constant of 12.441 angstroms was deposited on a samarium gallium garnet, Sm Ga O by chemical vapor deposition techniques. The lattice constant of the samarium gallium garnet was 12.436, which was smaller than that of the film by 0.005 angstrom. The resultant structure had a craze-free film which had bubble domains therein.

Examples II-IV Examples I-IV are listed below in the following table. In Example II, a [111] terbium iron garnet film was deposited in accordance with this invention on a gadolinium gallium garnet in which the film lattice constant exceeded the substrate lattice constant at room temperature by 0.065 A. The compressive stress due to the large lattice mismatch was relieved at the deposition temperature and the film is in tension due to the thermal expansion mismatch between film and substrate. This structure had no bubble domains in the film and also Had crazing on the film surface. In Example III, the film is again in tension leading to domains whose magnetization lies in the film plane. Example IV shows a film in compression but having negative magnetostriction and again there were no bubble domains, only domains whose magnetization lies from the group consisting of iron, iron and aluminum, in the plane.

TABLE Substrate lattice constant-film Example Lattice Lattice lattice Bubble Domains Grazing on No. Material l constant, A. Material I constant, A. constant, A. domain iii-plane film surface Stress I TbgFeson 12.441 SmaGa50 12.436 0.005 No None Compression. II TbgFe o 12.441 Gd Ga O 12.376 0.065 No Yes Yes-.- ension Tb3Fe50|2 12.441 NduasmmaGa on 12,452 +0.01]. N0 Yes None. D0. IV Y3Ga1.zFe3.gO 7 12.357 TbaGa o 12.347 -0.010 No Yes None Compression tllllorientation. b Positive magnetostriction constant.

B Negative magnetostriction constant.

We claim:

1. A method of producing a bubble domain containing film-substrate structure comprising the step of depositing a magnetic film of a single crystal material of the proper crystallographic orientation and having a positive magnetostriction constant on a substrate in which the magnetic film has a room temperature lattice constant which exceeds the room temperature lattice constant of the substrate at room temperature by an amount less than about 0.035 angstrom.

2. A method of producing a bubble domain containing single crystal iron garnet film-substrate structure comprising the step of depositing an iron garnet film of the proper orientation and having a positive magnetostriction constant on a substrate in which the iron garnet film has a room temperature lattice constant which exceeds the room :temperature lattice constant of the substrate by an amount less than about 0.035 angstrom.

3. A method as described in claim 2 whereby the room temperature lattice constant of the substrate exceeds the room temperature lattice constant of the film by an amount between 0.010 and 0.025 angstrom.

4. A method as described in claim 3 whereby the room temperature lattice constant of the substrate exceeds the room temperature lattice constant of the film by an amount between 0.015 and 0.020 angstrom.

5. A method as described in claim 2 whereby said film is deposited by a chemical vapor deposition technique.

6. A method of producing a bubble domain containing film-substrate structure comprising the step of depositing References Cited UNITED STATES PATENTS 3,617,381 11/1971 Hanak 117-235 3,525,638 8/1970 Archey 117-107.1 X 3,486,937 12/1969 Linares 117-235 X 3,429,740 2/1969 Mee 117-235 X 3,131,082 4/1964 Gambino 117-235 3,573,099 3/1971 Moore et a1 117-235 X 3,645,787 2/1972 Mee et a1. 117-240 3,645,788 2/1972 Mee et al 117-240 OTHER REFERENCES Giess et al., IBM Tech. Dis. Bull. pp. 517, I17-235, v01. 13, No. 2, July 1970.

WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner U.'S. Cl. X.-R.

117-106 R; 340-174 TF, 174 M UNITED STATES PATENT AND TRADEMARK GFFICE QERETIHCATE Q5 CQRREQTEGN PATENT NO. 3,745,046 DATED July 10, 1973 INVENTOR(S): Jack E. Mee, et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 3, line 2, change "substrate" to -film-;

line 3, change "film" to -substrate.

. Claim 4, line 2, change "substrate" to --film-;

line 3, change "film" to -substrate--.

Signed and Scaled this b Twenty-fifth Day of September I979 [SEAL] Arrest:

b LUTRELLE F. PARKER Arresting Oflicer Acting Commissioner of Patents and Trademarks 

